volume down + power button

Alternate Method

1. Press the Power button for 3 - 5 seconds.
2. Select Power off.
   If the device isn't responding proceed with step 3.
3. Remove/replace the battery.
4. Press and hold the Volume down key then press and hold the Power button for 3 to 5 seconds.
5. When the HBOOT screen appears, release the Volume down key.
6. Press the Volume key to select FACTORY RESET then press the Power button.
   This boot process takes several moments. If the device hangs or freezes, remove/replace the battery.
7. Perform Initial Activation/Setup.